Polyaniline-Modified Silver and Binary Silver-Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite-like silver particles were electrodeposited on Ti substrates from a supporting electrolyte-free 30 mmol?L-1 Ag(NH3)2+ solution, to synthesize the den-Ag/Ti electrode. Binary AgxCoy/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den-Ag/Ti electrode. Polyaniline (PANI) modified den-Ag/Ti and AgxCoy/Ti electrodes, PANI(n)-den-Ag/Ti and PANI(n)-AgxCoy/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)-Ag31Co69/Ti>Ag31Co69/Ti>PANI(20)-den-Ag/Ti>den-Ag/Ti. Among them, PANI(15)-Ag31Co69/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA?cm-2 at -0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.